This invention relates to point of operation safety devices for machines such as presses, spot welders, riveters and the like, having a ram which is forcefully moved to engage a workpiece upon command of an operator, for example, a press for installing fasteners or the like into sheeted plates. Point of operation safety devices of this type are disclosed in U.S. Pat. Nos. 3,315,049, 3,487,182 and 3,939,314.
All of the point of operation safety devices known to me for use on such machines before my invention hereof test or sense the work area with a probe prior to initiation of the cycle of the machine and allow the cycle to initiate only if no obstruction is detected by the probe in the work area. However, these previously known safety devices do not provide for halting or reversing the downward travel of the ram after its downward stroke has been initiated by the control circuit of the machine. This is a potentially dangerous condition, because in many such machines the workpiece is hand held by the operator and is occasionally not properly positioned when the cycle of the machine is started by the operator. When this occurs and is noted by the operator, the operator will sometimes try to re-position the workpiece before it is contacted by the ram.
If the operator does not succeed in properly repositioning the workpiece, and if there is no provision for stopping the downward stroke of the ram, injury to the operator and/or damage to the workpiece may result. The safety device of the present invention provides an electrical circuit arrangement in combination with the electrical control circuit for the electrical solenoid valves of the hydraulically or pneumatically controlled machines which will stop and/or reverse the downward stroke of the ram during any part of the cycle of the machine. If the control circuit valves are spring biased to the reverse position, the ram will be reversed by the circuit arrangement of this invention. However, if the control circuit valves are spring biased to a stop position for the ram, the ram will be stopped by the circuit arrangement of this invention.
It is desirable to stop and or reverse the downward stroke of the ram during any part of the cycle of the machine and this invention is directed toward doing so simply by raising the probe which is used to sense an obstruction in the patch of the ram. In addition, it is also desirable to stop and/or reverse the stroke of the ram by having the operator push up or down on the probe and in a modification of this invention an arrangement is provided whereby if the operator pushes either down or up on the probe the control circuit of the safety device will signal the control circuit of the press to stop or reverse the stroke of the ram.